Multi-channel antenna couplers or the like



Oct; 6, 1959 H. w. COWAN MULTI-CHANNEL ANTENNA COUPLERS OR THE LIKE Filed Nov. 26, 1954 HAROLD W. COWAN INVENTOR.

ms ATTORNEY alal. ll Ylru United States Patent MULTI-CHANNEL ANTENNA COUPLERS on THE LIKE Harold W. Cowan, Gardena, Calif, assignor to Hoffman Electronics Corporation, a corporation of California Application November 26, 1954, Serial No. 471,293

Claims. (Cl. 333-82) couplers for operation in the UHF and VHF frequency spectrums which serve to couple a plurality of transmitters and/or a plurality of receivers to a single antenna. The design of a couple should: provide for coverage of the desired frequency spectrum, insure adequate isolation between resonators in order to minimize the interaction between equipments, match the impedance of conventional 50 ohm transmission lines to the antenna impedance to assure a standing wave ratio less than 2, and be physically compact and of relatively simple yet sturdy manufacture. Multi-channel antenna couplers presently in use are almost entirely of the series-coupled variety in' wliich the channel resonator plurality is coupled along the length of a conventional 50 ohm coaxial cable which leadsto the transmitting and receiving antenna. Unfortunately, the series-coupled system has several deficicncies among which are its large physical size, its menswear complexity, and the relatively wide adjacentchannel frequency separation which is necessary to maintain adequate isolation of the several channels one from another; I

'Durin g the very recent past, certain British and United States antenna coupler manufacturers have made .various' attempts to design a suitable antenna coupler in which theseveral channel resonators are coupled in parallel, inter se, to the antenna coaxial lead-in line. Attempts taking the direction toward parallel resonator couplers have heretofore been almost fruitless, owing principally to the fact that adequate inter-channel isolation is almost impossible'to attain. In addition, design problems render it difiicult to suitably match each coupler resonator to its associated equipment feed-in line without seriously afi e cting a preset match existing with respect to adja-' cent channel resonators and their associated equipments when such channels have a narrow frequency separation;

For all practical purposes, it may safely be stated that the electronics industry has not heretofore devised a parallel multi-ch'annel antenna coupler which offers complete satisfaction. v Therefore, it is an object of the present invention to provide a new and useful parallel multi-channel antenna coupler.

It is a further object of the present invention to provide a new and useful parallel multi-channel antenna coupler which will be compact and exhibit optimum performance. ,:According to the present invention, a plurality of parallel coupled cavity resonators surround an antenna leadin line and are each equipped with reentrant, adjustable, teles copic, tuning elements which are capable of either manual or remote adjustment or are adaptable for coupling to a mechanical self-tuning unit. Each cavity has a capacity-coupled input the capacitance value of which is made to' decrease automatically with in creases in operating frequency so as to assure higher cavity Qs and maintain high level channel isolation de-' spite increases in operating frequency. In addition, each"- cavity is equipped with a high impedance output antenna coupling loop which may be adjusted'for a desired complex coupling coefiicient and" a consequent impedance match between source and'load.

' The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation,- together with further objects andadvantages thereof, may best be understood by reference to the following description, taken in connection. with the accompanying drawings, in

which: p

1 Figure 1 is an elevational view, partially cut away,

(if a multi-channel antenna coupler according to the present invention.

' Figure 2 is a top view of the multi-channel antenna coupler shown in Figure 1.

T Figure 3 is a detailed perspective view of the impedance matching adjustment mechanism of each cavity resonator in the multi-channel antenna coupler "shown in Figure 'l. Figure 4 is a bottom view of the multi-channel anten=' na coupler shown in Figure l.

i In Figure 1 each of four cavity resonators 10 is pro vided with an electrical connector, coaxialline receptacle 11 adjacent outer wall surface 23- and at least the center pin of which is electrically connected through cavity wall' admittance aperture 25 to tapered metallic element 12. Metallic element 12 is disposed to lie in close proximity to inner wall surface 24 of cavity resonator 10 but is in sulated therefrom by means of fixture 13 a d ce aijiic head eyebolt 14. Vertically movable' telescopic element 15' is axially aligned with respect to central axis X X of cavity resonator 10 and isenca'sedwithin seating ele ment 16. The combination of elements' l5 and 16,fr'or'n a functional point of view, may be considered to constitute an adjustable-length re-entrant 'device for tuning Tuning knob 17 is mechanically cou-' pled in a conventional manner to telescopic element 15 so that the appropriate rotation of tuning knob 17 will accomplishment.

produce the desired protrusion of element 15 from seating element 16. Tuning knob 17 "may be'provided with pointer 18, in order to enable frequency calibration for each resonator. In lieu of tuning knob 17, telescopic element 15 may be appropriately coupled to a suitable self-tuning mechanismor otherremotely controlled de vice. Antenna lead-in-line '19is' disposed in the center of the configuration formed by cavity resonators 10.. Impedance matching manual" controls '20 appropriately couple each cavity r'es'onator'lO' to antenna transmission line 19. Sliding contacts'ZZ intercouple the center con ductor of antenna feed-in line 19 to the quarter-wave length coupling elements (described in- Figure" 3) of each cavity resonator. All of the controls and the cavity resonators and associated antenna transmission line are affixed to mounting base 21. a

Figure 1 will serve to illustrate the operation of telescopic element 15 and the effect of the capacity offered by a'relatively long, thin, appropriately tapered metallic element 12.. For a given'o'perating frequency setting,- determined of course by cavity dimensions'and by the relative amount of protrusion of telescopic element 15 from seating elementlfi, a certain amount-of capacitance will be contributed to the resonator 10' construction by virtue of the capacitance existing between .element. 12 and the inner wall of cavity resonator. 10 and .also-between ele ment 12.:and theelfectivereentrant portion ofthe cavity consisting of telescopic element 15 and seating element l atented Qeti e, 1959 16.. Let it be assumed that it is desired to increase the operating frequency of cavity resonator 10. In such a case, telescopic element 15 will be withdrawn at least slightly into seating element 16 so that the capacitance existing between element 12 and telescopic element 15 will be reduced. At the outset it would appear that the input capacitive reactance attributed by element 12 would decrease, by virtue of the increased operating frequency. However, the effect of the increased operating frequency will be more than overcome by the decrease in capacitance between element 12 and telescopic element 15, with a resulting increase in capacitive reactance, so that the over-all effect will be to increase the effective input capacitive reactance offered by element 12. Thus, cavity resonator 10 in conjunction with capacitive element 12 may be considered as a parallel resonant circuit shunted by a high capacitive reactance in series with the source impedance and source voltage generating source. It is at once seen that as the capacitive reactance increases, the resistance portion of the source impedance will be less able to reduce the Q, or factor of merit, of the cavity resonator. Hence, for increasing operating frequencies the Q of cavity resonator 10 will increase, and thus tend to preserve adjacent channel isolation. The effectiveness of the above feature will be enhanced by selecting an appropriate taper for element 12. T illustrate the eifectiveness of the applicants method of providing increasing cavity resonator Qs for increased operating frequencies, experimentation has shown that the multi-channel antenna coupler described herein will maintain a channel isolation of 15 decibels, in the frequency range of 230 to 390 megacycles, where adjacent channel separation is only in the order of 3 megacycles. Further, this desirable performance is accompanied by an extremely low inser tion loss of the order of /2 decibel.

Figure 2 displays a top view of the multi-channel antenna coupler shown in Figure 1. Apertures 200 are cut into base 21 so that each impedance matching loop structure 201 may be rotated into and away from the interior of its associated cavity resonator.

Figure 3 shows a portion of the cutout area of each cavity resonator and also a segment of coupling loop or impedance matching device 300. Casing 301 of coaxial antenna feed-in line 302 is slotted longitudinally to admit the edge of wall lip portion 303. The remaining lip portion 308 associated with the slotted aperture (which admits impedance matching device 300 into the interior of its associated cavity) is soldered, seam-welded, or otherwise afiixed to the outer wall area of an adjacent cavity resonator. Elements 304 (disposed at both ends of device 300) afiix element 305 of impedance matching device 300 to rotatable shaft 306 (made of an insulation material), which is in turn affixed to control 20 of Figure 1. Elements 304 may have a substantially straight configuration rather than the curved configuration shown. At all events, the coupling loop or device 300 may be considered to define a plane including or bisecting element 305 and including pivot axis Y-Y. Thus, by rotating shaft 306 one may vary the angle subtended by the plane previously mentioned and a plane including axes XX (see Figure 1) and YY (which of course constitutes the intersection of the two planes). Traveling shorting element 307 shorts to ground probe 305 at a point an electrical one-quarter wave length from the connection of element 305' to coaxial antenna lead-in 302. All of the coupling probes may be chosen to be an electrical one-quarter wave length long at mid-frequency so that the point of coupling to the antenna lead-in line will be a high impedance point, in order that a maximum energy level is capable of transmission.

The apparatus shown in Figure 3 operates as follows. Impedance matching device 300 may be rotated in and out of cavity resonator by means of turning matching control 20, shown in Figure 1. The object of rotating quarter-wave length element 305 in and out of cavity resonator 10 is to vary the magnetic coupling between cavity resonator 10 and coaxial antenna feed-in line 302. By choosing an optimum position for impedance matching device 300, an optimum magnetic flux coupling coeificient will be achieved so that cavity resonator 10 will provide a suitable impedance match between the antenna and the equipment connected to receptacle 11 (see Figure 1).

Figure 4 displays a bottom view of the multi-channel antenna coupler shown in Figure 1. From Figure 4 it is seen that each cavity resonator will be supplied with a tuning knob 400 and an impedance matching control 401. Signal energy is taken from the cavity resonators and is coupled through sliding contacts 22 (see Figure 1 for a side view of contacts 22) to the input end of antenna feed-in line 19 (see Figure 1).

Experimentation has shown that the applicants invention as above described is capable of operating over any part or all of the VHF and UHF spectrums. Over any chosen operating frequency band, each cavity of the aforementioned coupler is capable of maintaining a bandwidth response which is independent of the operating center frequency while simultaneously providing an impedance match between the source and load associated therewith. This bandwidth independence is an important feature of this invention.

While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this in vention.

I claim:

1. A cavity resonator including, in combination, a cavity wall having inner and outer wall surfaces and an interiorly disposed central axis, said cavity wall being provided with an electrical connector admittance aperture and also a longitudinally oriented slotted aperture, a base affixed to said cavity wall and disposed transversely with respect to said central axis, a first electrical connector affixed to but insulated from said outer wall surface and passing through said electrical connector aperture for electrical connection within said cavity resonator, a relatively long thin coupling element coupled to said first connector and disposed in proximity to but insulated from said inner wall surface of said resonator, a cavity tuning element of adjustable length supported from said base of said resonator along said central axis thereof, an antenna connector fixedly disposed with respect to said base, an antenna coupling loop supported for movement into and out of said resonator through said slotted aperture, and means coupling said antenna loop to said antenna connector.

2. A cavity resonator including, in combination, a cavity wall having inner and outer wall surfaces and an interiorly disposed central axis, said cavity wall being provided with an electrical connector admittance aperture and also a longitudinally oriented slotted aperture, a base affixed to said cavity wall and disposed transverse ly with respect to said central axis, a first electrical connector affixed to but insulated from said outer wall surface and passing through said electrical connector aperture for electrical connection within said cavity resonator, a relatively long thin coupling element coupled to said first connector and disposed in proximity to but insulated from said inner wall surface of said resonator, a cavity tuning element of adjustable length supported from said base of said resonator along said central axis thereof, an antenna connector fixedly disposed with respect to said base, an antenna coupling loop supported for movement into and out of said resonator through said slotted aperture, and rotationally slidable means coupling said antenna loop to said antenna connector.

3. A multi-channel antenna coupler including, in combination, a mounting base; a plurality of cavity resonators each having a central axis, a cavity wall, and at least one aperture provided in said cavity wall, said cavity resonators being disposed upon and aifixed to said mounting base in such manner that the said axes thereof are perpendicular to the plane of said mounting base; a plurality of adjustable-length re-entrant devices each being axially disposed Within one of said cavity resonator; a plurality of means each being afiixed to one of said re-entrant devices for varying as desired the length thereof; a plurality of coaxial input receptacles having a central connector, each receptacle being aflixed to one of said cavity resonators; a plurality of metallic elements each being electrically connected to an associated receptacle central connector and being disposed within but insulated from one of said cavity resonators; a plurality of coupling loops each being movable within and without one of said cavity resonators through an associated one of said apertures; a plurality of means affixed to said base for selectively rotating each of said loops into and out of one of said cavity resonators; and a coaxial antenna feed-in line coupled to one end of each of said loops, the remaining end of each of said loops being electrically connected to the said wall of its associated cavity resonator.

4. Apparatus according to claim 3 in which said cavity resonator plurality is circularly disposed upon said mounting base.

5. Apparatus according to claim 4 in which each of said metallic elements is positioned parallel to the said axis of its associated cavity resonator.

'6. Apparatus according to claim 4 in which said apertures are slotted, longitudinally disposed, and defined by first and second wall lip portions, said first lip portion being afiixed to an adjacent resonator, said second lip portion being affixed to said coaxial antenna feed-in line.

7. Apparatus according to claim 6 in which each of said metallic elements is positioned parallel to the said axis of its associated cavity resonator.

8. Apparatus according to claim 4 in which each, of said metallic elements is positioned parallel to a corresponding one of said re-entrant devices.

9. Apparatus according to claim 3 in which each of said metallic elements is positioned parallel to the said axis of its associated cavity resonator.

10. Apparatus according to claim 6 in which each of said coupling loops is pivotally secured to a corresponding said second lip portion and has a pivot axis parallel to said central axis, said pivot and central axes defining a first plane, said loop substantially defining a second plane which includes said pivot axis, means for rotating said loop about said pivot axis for adjusting the angle subtended by said first and second planes, said loop being grounded to said cavity wall, said cavity resonators each further including a slidable shorting element disposed upon said loop and adapted for electrical contact with said second lip portion for all dispositions of said loop.

References Cited in the file of this patent UNITED STATES PATENTS 2,373,233 Dow et a1. Apr. 10, 1945 2,498,073 Edson et a1 Feb. 21, 1950 2,562,921 Kandoian Aug. 7, 1951 2,603,754 Hansen July 15, 1952 2,715,211 Murakarni Aug. 9, 1955' 2,762,017 Bradburd et al. Sept. 4, 1956 

